摘要:

AbstractSurface air temperature records from stations on the west coast of the Antarctic Peninsula show a higher degree of interannual variability and stronger long‐term warming trends than recorded elsewhere in Antarctica. Possible mechanisms for driving these fluctuations are investigated. The extreme climatic sensitivity of this region may be linked to a stronger coupling between temperatures and regional sea‐ice extent than is seen elsewhere in Antarctica. Significant interannual persistence of air temperature anomalies suggests a link with ocean temperatures or circulat

ISSN:0899-8418    

DOI:10.1002/joc.3370140402

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe principal component regression approach is used for forecasting the monthly 700 hPa geopotential fields over India, for July, from the geopotential fields observed during June. The data used are for the 23‐year period from 1958 to 1980. The multiple linear regression equations are developed on 22 years of data using the principal components as predictors and keeping one randomly selected year for independent testing. The forecasts and validation experiments are carried out for seven representative years. The results show some skill in forecasting the monthly height fields over Indi

ISSN:0899-8418    

DOI:10.1002/joc.3370140403

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractWe review and compare two alternative spatial regression methods used in dendroclimatology to reconstruct climate from tree rings. These methods are orthogonal spatial regression (OSR) and canonical regression (CR). Both the OSR and CR methods have a common foundation in least‐squares theory and converge to the same solution when allpcandidate tree‐ring predictors of climate are forced into the model. However, the perfomance of OSR and CR may differ when only subsetsp′

ISSN:0899-8418    

DOI:10.1002/joc.3370140404

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractInfluences of varying rain‐gauge networks on continental and terrestrial precipitation averages (derived from data observed on those networks) are evaluated. Unsystematically and systematically designed station networks are considered, the latter being represented by the NCAR World Monthly Surface Station Climatology, which contains hand‐picked but time‐varying networks that date back to the 1800s. Biases arising from spatially uneven and temporally variable precipitation‐observing networks can be significant.For all the continents, except South America, sparse rain‐gauge networks produce overestimates of continental mean precipitation. Mean precipitation for South America, in contrast, is underestimated substantially by low densities of observing stations. Sampling errors tend to be large in areas of high precipitation and in regions with strong spatial precipitation gradients (e.g. in the Sahel). These patterns occur whether the station network has been selected systematically (as in the NCAR network) or unsystematically.Systematic sampling of mean precipitation (at the NCAR station locations), however, suggests that many yearly NCAR station networks are adequate for estimating continental average precipitation. As early as 1890, NCAR networks for Australia resolve continental average precipitation accurately. Not until 1960, however, do NCAR networks for South America begin to resolve continental mean precipitation adequately. Regional and continental NCAR network errors also tend to cancel one another, often giving accurate yearly estimates of terrestrial mean prec

ISSN:0899-8418    

DOI:10.1002/joc.3370140405

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractTemporal and spatial variations of the Northern Hemisphere's circumpolar vortex are analysed for each January from 1947 to 1990. Our data set is developed by digitizing the 546‐dam isoheight from 50‐kPa charts and recording the latitude of this contour at each 10° meridian. Principal components analysis is applied to the resulting 699‐day by 36‐variable matrix to examine the temporal and spatial evolution of the circumpolar vortex.The first principal component is comparable to the Pacific‐North America (PNA) teleconnection pattern. Over the 44 Januarys analysed, the frequency of the positive phase of the PNA pattern has increased. Principal component 2 is similar to the Eurasian pattern and varies between axially asymmetric zonal flow and a three‐wave pattern centred over the pole. The asymmetric pattern, which is characterized by higher heights over western Europe and Scandinavia, has increased in frequency over the study period. With the third principal component, which is similar to the East Atlantic teleconnection pattern, the strength of the Icelandic Low varies markedly. Time series of scores on the third component indicate that 50‐kPa heights over the North Atlantic are lower over the past 20 years. The fourth principal component is related to vortex area. The northern vortex has occupied a more expanded position since the mid‐1960s. These first four principal components explain half of the total variance in the data.In toto, these results indicate that the January circumpolar vortex has expanded over the past two decades. Most of the expansion has occurred in the vicinity of the Aleutian Low and has produced increased meridional flow throughout much of the Western Hemisphere. This circulation change could account for the observed increased occurrence of warm air masses in winter over eastern Alaska and western Canada, increased cyclone occurrence in the north‐western Atlantic, and both the increased frequency of Arctic outbreaks and declining temperatures in the south‐eastern USA. The overall vortex expansion is contrary to general circulation model forecasts that predict a decrease in the meridional temperature gradient of the Northern Hemisphere as trace‐gas c

ISSN:0899-8418    

DOI:10.1002/joc.3370140406

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractOcean‐atmosphere heat fluxes were calculated from marine weather reports over a mesoscale region of the Coral Sea near Townsville, Australia. These heat fluxes were compared, as 5‐week averages, with a set of heat fluxes derived over the same region from a combination of satellite and surface data. These satellite‐ and surface‐derived fluxes were calibrated and validated against accurate, independent surface heat fluxes, as described in a previous paper.Significant differences were noted between the two sets of heat fluxes. The discrepancies in the net solar radiation are attributed to insufficient marine weather reports and/or improper cloud parameterization in the formulae applied to the marine data. Some large differences were observed in the outgoing turbulent heat fluxes, and these were traced to higher water‐air specific humidity gradients in the marine data. These two discrepancies cancel so that the long‐term (45 week) averages of the total ocean‐atmosphere heat flux, at 52 W m−2for the satellite‐based technique and 34 W m−2for the shipboard method, differ by only 18 W m−2.On the basis of these systematic differences it was concluded that the heat fluxes derived from satellite and surface data in this study were superior in quality and reliability to heat fluxes calculated from marine weather reports. Further studies are required to test this resu

ISSN:0899-8418    

DOI:10.1002/joc.3370140407

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractAir mass analysis, though widely used in early atmospheric studies, has seldom been employed in recent decades. In part, this may be due to the lack of agreement on a quantitative air mass classification technique. Synoptic analyses (of which air mass analysis is one example) have much potential for examining the relationships among a variety of surface processes and climate. Schwartz (1991) proposed an integrated air mass classification system that was able to overcome some of the limitations of previous methods. This study further validates that approach by quantitatively linking these air masses to 500‐hPa height and surface pressure patterns. Cluster analysis was used with daily and average monthly air mass distributions in the north‐central USA to identify similar groups. For the daily analyses, average 500‐hPa height, surface pressure, and air mass percentage coverage patterns were determined for the groups in each season. In the monthly analyses, transects of 500‐hPa height difference were examined with the multiple analysis of variance (MANOVA) technique in order to detect significant changes relative to the clusters. Our results show that: (i) integrated‐method air mass percentage coverage distributions can be related quantitatively to a small number of meaningful 500‐hPa height and surface pressure patterns in all seasons; (ii) key transects can be used to describe changes in average monthly air mass dominance and 500‐hPa flow patterns from one year to another; and (iii) for the period 1958–1981, cool air masses decreased in frequency over the study area during sp

ISSN:0899-8418    

DOI:10.1002/joc.3370140408

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractHeat balance calculations indicate that during the last 40 years a marked decrease in the evaporation rate from the Dead Sea has accompanied its increased salinity. Two‐thirds of the estimated 17 per cent decrease is attributed to the reduced vapour pressure of its now salt‐saturated waters, the remaining one‐third to the reduction in radiation balance caused by the greater longwave loss from its warmer sea surface. The rate of evaporation from a hypothetical Dead Sea with a surface level restored to previous levels by an influx of Mediterranean waters was estimated to be 158 per cent of its current rate, which is 1.05 m per year. Two‐thirds of this increase was attributed to the greater vapour pressure gradient between the less saline surface water and the atmosphere, one‐third to the increased radiation balance at its cooler sea surface. Although the mechanism for these changes are well understood and easily calculated, a number of complex interactions exist between the various effects that do not allow a quantitative relationship to be established analytically between the Dead Sea's surface level or salinity and rate of evaporation. However, empirically, the linear relationship between annual evaporation,E(m year−1), and surface density,D(g cm−3),E= 4.701 ‐ 2.926D.accounts for 98 per cent of the variation between evaporation from a salt‐free and from a salt

ISSN:0899-8418    

DOI:10.1002/joc.3370140409

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370140410

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370140411

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY